In most of the existing dental clinics of today, both a dental surgeon and his or her assistant generally work on an equal-levelled floor surface area of a dental treatment room, thus being more often than not put to such difficulties that the surgeon, while treating a patient, unexpectedly happen to touch the assistant on the head, elbow or toes, and vice versa. In order to avert from the difficulties, the dentist cannot but always attend delicately to the assistant's seated position and working manner. Likewise the assistant is also forced to work as reservedly as possible so as not to touch the dentist, thus both of them being unable to concentratively treat the patient to their fullest satisfaction.